1. Field of the Industrial Application
The present invention relates to a differential amplifier comprising transistors which are differentially coupled.
2. Description of the Prior Art
Conventional differential amplifiers are shown in FIGS. 1 and 2. In FIG. 1, Q1 and Q2 are differentially coupled PNP type transistors which are connected to a current mirror circuit 1. The current mirror functions as a collector active load which comprises a diode D1, a transistor Q5, and resistors R1 and R2. The value at the collector of transistor Q2 (one of the differentially coupled transistors) functions as the system output and Q2 operates as an outputting transistor. A PNP type transistor Q4 is connected at a point between the collector of the transistor Q1 and the current mirror circuit 1. Namely, the emitter of Q4 is connected with the collector of Q1, the collector of Q4 is connected with the current mirror circuit, and the base of Q4 is connected to ground.
In FIG. 2, a parallel circuit which comprises a resistor R3 and a condenser C1, is connected at the point between the transistor Q1 and the current mirror circuit 1 instead of the transistor Q4.
In addition, in FIGS. 1 and 2, a current generator 2 is connected with a common emitter of the coupled transistors Q1 and Q2 which are differentially connected. A voltage source +B is applied to the current generator 2 and a voltage source -B is applied to the current mirror circuit 1.